The present invention relates to a method and tubular reactors for producing a product mixture from a reactant mixture. More specifically, the present invention relates to improving heat transfer in tubular reactors.
Reactors containing packings with catalyst have been described, for example, tubular reactors used in steam methane reforming. The packings may be random packings such as catalyst pellets or so-called structured packing. Structured packing, as compared to random packings, can produce lower pressure drop, are not easily fluidized, and are not prone to settling or crushing. Since tubular reactors are often externally heated or cooled, another important characteristic of the reactor is related to heat transfer between the external heat source/sink and the process fluid within the reactor.
Tubular reactors may contain random packing or structured packing where the packing includes catalyst for the desired reaction. Structured packing has been credited with lower pressure drop compared to random packing.
Heat transfer in tubular reactors has been recognized as being important. Efforts relating to improving heat transfer in tubular reactors have been described.
Davidson, U.S. Pat. No. 4,340,501, describes a structure in a reactor vessel where the fluid is intermittently but controllably brought into contact with the vessel walls. As a result, Davidson states that it is possible to obtain the smooth-flow characteristics of honeycomb structures with the heat transfer characteristics of particulate beds.
In the invention according to Davidson, the process for contacting a fluid with the walls of a vessel is characterized by causing the fluid to flow alternatingly (a) through a structure within the vessel, and (b) through a space between the structure and the vessel walls. Davidson also describes an apparatus for carrying out the process comprising a vessel and a structure inside the vessel.
Repasky et al., U.S. Pat. Pub. No. 2007/0297956 discloses a method and a reactor made by a method for increasing heat transfer in a tubular reactor with a structured packing. The approach is to expand the structure toward the tubular reactor wall during construction, thereby reducing the gap between the wall and the packing. The fluid is squeezed between the packing and the tube wall. The reduced gap increases the velocity of the fluid and thereby increases heat transfer.
A problem with this approach and any approach where heat transfer relies on the gap between the structure and the tube wall, is that after extended operation at high temperature and pressure, the tube may experience time-dependent plastic deformation, commonly known as “creep,” resulting in an increase in the tube diameter and a corresponding increase in the gap between the tube wall and the structured packing. Since the mechanism for heat transfer relies on the velocity of the fluid in this gap, and the velocity decreases as the gap is increased, the heat transfer decreases when the tube creeps. When heat transfer is reduced the reactor performance decreases.
It would be desirable to maintain heat transfer efficiency in a tubular reactor throughout the life of the tubular reactor especially when the tube creeps. The present invention solves the problem of heat transfer degradation resulting from tube creep in a tubular reactor.